The present invention relates to a method for examining objects using ultrasound according to reflection processes, in particular 3D scanning, wherein the respective object is scanned with an ultrasound transducer with associated transmit/receive unit appropriate for volume scanning and the obtained echoes are stored in a volume memory with reference to the spatial coordinates of the reflection points, from which memory they are accessed according to selectable accessing criteria and can be forwarded to an evaluation unit, in particular a display unit.
Such methods have been known for quite some time and are documented in AT 385 155 B, for example, which relates to expanding the ultrasound cross-sectional image recording (B-image), wherein a sound beam is swiveled in a plane, thus recording a cross-sectional image. To obtain the information along an idealized beam a focused sound wave is emitted which is partially reflected by the object structures as it penetrates into the object being examined, generating echoes which are evaluated according to the flight timexe2x80x94this determines the distance of the echo to the transducerxe2x80x94and according to the amplitude which determines the brightness of the B-image mode. With the well-known Doppler method changes in frequency are recorded and thus the direction of flow or flow rate in blood vessels is determined. The total of all assessed information as well as position information of the swiveling transducer create the ultrasound image. The repetition rate by which a specific part of the object is rescanned results from the maximum desired penetration depth and the number of scan lines per image. At a required penetration depth of 20 cm a period of approximately 260 microseconds elapses, until echoes are received from the maximum penetration depth on the transducer. If an ultrasound image comprises 200 scanning beams, then a specific area can be scanned about 20 times per second. For 3D-scanning, the cross-sectional plane is swiveled in perpendicular direction over the volume of interest, such that if for instance 200 images corresponding substantially to the B-image in different positions are to be obtained from the volume each part of the volume is rescanned only once in 10 seconds with the above mentioned assumptions, leading to prolonged scanning times for recording of a volume and in the case of moving objects, the movement in a given volume area can be viewed only disjointedly.
For increasing the scanning density it is known to generate multiple scan lines from each emitted ultrasound wave when the echoes are being received, whereby usually four scan lines are processed In parallel, though for cardiological applications more than four lines can be processed. These techniques can be transferred to three-dimensional scanning, but not with total success, as evident from the above mentioned example.
For scans which combine different modalities, such as a B-image of the tissue and color Doppler imaging of blood flow, the scanning sequence, rigid in terms of time and location with B-images, is modified. A sequence of adjacent beams for B-mode scanning is interrupted by a sequence of ultrasound beams in a different position for Doppler evaluation. Also this method makes no consideration of movement of the object and follows a temporal and local sequence.
The aim of the present invention accordingly is to create a novel method which results in improved utilization of time used or to be used in ultrasound scanning, in particular with 3D scanning, without important information being lost.
This object is obtained according to the invention with a reflection method for the ultrasound examination of an object, which comprises the steps of 3D scanning the volume of the object with an ultrasound transducer associated with a transmit/receive unit and suitable for 3D volume scanning to obtain information constituted by echo signals, storing the obtained echo signals information in a 3D volume memory in clear assignation to the local coordinates of the echo signals, accessing the local coordinates from the 3D volume memory according to selectable accessing criteria, and forwarding the local coordinates to an evaluation unit. The spatial line density and/or the temporal repetition frequency, in which certain areas of the volume are scanned to obtain the information, is derived from this information in such a form that the areas having a lower information density are scanned more seldom and/or with less scanning density than the areas of higher information density, for which purpose a computer generates informations about the information density received from the same areas of the volume at different times, and controls a control unit for adjusting the repetition frequency and/or the local scanning density, the control unit determining the location and timing of individual scanning instances.
The fundamental idea of the invention is to detect those areas within a volume to be examined, which have the least temporal and/or local changes and/or also the least information density and to restrict the number of scan-lines and scan-planes and their density to the required values. For example, in the case of pregnancy examinations the amniotic fluid area can be scanned with less line density and less frequently, whereby on the other hand areas with higher density of detail, such as soft tissue and areas with rapid image content change such as movement and organs, are scanned more often and more densely. The basic rule here will be the image change which actually occurs between two or more scans.